Fecal pellet and egg production rates of copepod species at varying suspended sediment concentrations

We investigated the effect of suspended sediments on the vital rates of the copepods Calanus finmarchicus, Pseudocalanus sp. and Metridia longa in a Greenland sub-Arctic fjord. The fjord had a gradient of suspended particulate matter (SPM) with high concentrations (>50 mg/L) in the inner fjord due to glacial melt water runoff. Laboratory experiments showed that when feeding on the diatom Thalassiosira weissflogii specific ingestion rates were low at high concentrations of suspended sediment for C. finmarchicus (>20 mg/L) and Pseudocalanus sp. (>50 mg/L), while no effect was found for M. longa. For C. finmarchicus, a relatively constant fecal pellet production (FPP) and fecal pellet volume suggested ingestion of sediment, which probably led to reduction in egg production rates (EPRs) at high sediment concentrations. For Pseudocalanus sp., FPP decreased with increasing sediment concentrations, while no effect was observed on EPR. No significant difference was observed in FPP for M. longa feeding on the diatom T. weissflogii compared to the ciliate Strombidium sulcatum. The study shows that high sediment concentrations influence the capability of carbon turnover in C. finmarchicus and Pseudocalanus sp., while M. longa appears to be more tolerant to high sediment loads. Therefore, high concentrations of SPM could potentially influence the species composition of glacially influenced fjords.

Macrobenthic abundance, biomass, productivity and production in the deep Arctic ocean

The few existing studies on macrobenthic communities of the deep Arctic Ocean report low standing stocks, and confirm a gradient with declining biomass from the slopes down to the basins as commonly reported for deep-sea benthos. In this study we have further investigated the relationship of faunal abundance (N), biomass (B) as well as community production (P) with water depth, geographical latitude and sea ice concentration. The underlying dataset combines legacy data from the past 20 years, as well as recent field studies selected according to standardized quality control procedures. Community P/B and production were estimated using the multi-parameter ANN model developed by Brey (2012). We could confirm the previously described negative relationship of water depth and macrofauna standing stock in the Arctic deep-sea. Furthermore, the sea-ice cover increasing with high latitudes, correlated with decreasing abundances of down to < 200 individuals/m**2, biomasses of < 65 mg C/m**2 and P of < 75 mg C/m**2/y. Stations under influence of the seasonal ice zone (SIZ) showed much higher standing stock and P means between 400 - 1400 mg C/m**2/y; even at depths up to 3700 m. We conclude that particle flux is the key factor structuring benthic communities in the deep Arctic ocean, explaining both the low values in the ice-covered Arctic basins and the high values along the SIZ.

Phytoplankton biomass, chlorophyll concentration, and variability of lipid content in Calanus euxinus in the Black Sea in June 1991

During field studies relationships between chlorophyll concentrations, phytoplankton biomass (total, individual sizes and species) and level of accumulation of total lipids, wax esters, triacylglycerols, and phospholipids in C. euxinus (copepodites V and females) were studied. These relationships allowed to display not only simple trophic relations between isolated parts of the C. euxinus population and phytoplankton, but also selective role of individual algae species in forming lipid reserves too. Besides it was found that geographical variability of chlorophyll concentration and phytoplankton biomass correlates closely only with those lipid fractions (wax esters and phospholipids) of C. euxinus, which accumulated and kept in a body for a fairly long time. No correlation was found between phytoplankton and for rapidly metabolized triacylglycerols, which have to be utilized within few hours.

Zooplankton carbon budget from Trondheim mesocosm experiment

We measured respiration, egg production and fecal pellet production of five common copepod species, when fed on suspended or aggregated food from two mesocosm, + NP and + NPSi. We hypothetised that calanoid copepods (Temora longicornis, Acartia spp., Centropages spp.) would feed mainly on suspended food, and have low respiration and egestion rates when food was only available as aggregates, while harpacticoids and Oncaea spp. would mainly feed on aggregated food and have low metabolic rates when only suspended food was available. Copepods were collected from the lagoon, and adapted to experimental conditions for 24 h. Food suspension was collected from the mesocosms, and either offered to copepods directly (suspended food) or after rotating in a plankton wheel until most phytoplankton was aggregated together (aggregated food). After 24-h incubation we counted the produced eggs and pellets, and measured copepod respiration using microelectrodes.

Experimental assessment of sediment burial in eelgrass Zostera marina in Kiel Bight

Seagrass meadows, one of the world's most important and productive coastal habitats, are threatened by a range of anthropogenic actions. Burial of seagrass plants due to coastal activities is one important anthropogenic pressure leading to the decline of local populations. In our study, we assessed the response of eelgrass Zostera marina to sediment burial from physiological, morphological, and population parameters. In a full factorial field experiment, burial level (5-20cm) and burial duration (4-16 weeks) were manipulated. Negative effects were visible even at the lowest burial level (5 cm) and shortest duration (4 weeks), with increasing effects over time and burial level. Buried seagrasses showed higher shoot mortality, delayed growth and flowering and lower carbohydrate storage. The observed effects will likely have an impact on next year's survival of buried plants. Our results have implications for the management of this important coastal plant.

Carbon cycling in the northern Humboldt Current off Chile

The structure of the zooplankton foodweb and their dominant carbon fluxes were studied in the upwelling system off northern Chile (Mejillones Bay; 23°S) between October 2000 and December 2002. High primary production (PP) rates (18 gC/m**2 d) were mostly due to the net-phytoplankton size fraction (>23 µm). High PP has been traditionally associated with the wind-driven upwelling fertilizing effect of equatorial subsurface waters, which favour development of a short food chain dominated by a few small clupeiform fish species. The objective of the present work was to study the trophic carbon flow through the first step of this 'classical chain' (from phytoplankton to primary consumers such as copepods and euphausiids) and the carbon flow towards the gelatinous web composed of both filter-feeding and carnivorous zooplankton. To accomplish this objective, feeding experiments with copepods, appendicularians, ctenophores, and chaetognaths were conducted using naturally occurring plankton prey assemblages. Throughout the study, the total carbon ingestion rates showed that the dominant appendicularian species and small copepods consumed an average of 7 and 5 µgC/ind d, respectively. In addition, copepods ingested particles mainly in the size range of nano- and microplankton, whereas appendicularians ingested in the range of pico- and nanoplankton. Small copepods and appendicularians removed a small fraction of total daily PP (range 6-11%). However, when the pico- + nanoplankton fractions were the major contributors to total PP (oligotrophic conditions), grazing by small copepods increased markedly to 86% of total PP. Under these more oligotrophic conditions, the euphausiids grazing increased as well, but only reached values lower than 5% of total PP. During this study, chaetognaths and ctenophores ingested an average of 1 and 14 copepods/ind d, respectively. In terms of biomass consumed, the potential impact of carnivorous gelatinous zooplankton on the small-size copepod community (preferred prey) was important (2-12% of biomass removed daily). However, their impact produced more significant results on copepod abundance (up to 33%), which suggests that carnivorous gelatinous zooplankton may even modulate (control) the abundance of some species as well as the size structure of the copepod community.